I woke up at 3:43 one morning. After an hour of lying awake in the dark, I moved to the sofa and read my book for an hour. Then I turned off the light and went back to sleep.

Middle-of-the-night awakenings are common for many people, and how we deal with this habit is key to getting a good sleep, says sleep expert Michael Grandner, a psychologist at the Center for Sleep and Circadian Neurobiology at the University of Pennsylvania. It turns out that I made a couple of mistakes that might have kept me from going back to sleep more quickly: I shouldn't have looked at my clock, and I shouldn't have waited so long to get out of bed.

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Looking at the clock leads to two things antithetical to sleep, Grandner says -- math and worry. You are bound to calculate how many hours of sleep you've gotten and how many are left, thereby triggering daytime brain functions. You are likely to then start worrying about being tired tomorrow as you tackle a long to-do list, thereby activating stress.

Staying in bed while awake trains you to associate your bed with wakefulness rather than sleep, Grandner says.

Those are just two bits of sound sleep advice, but why did I wake up in the rst place? That's a question in sleep research that remains largely unanswered.

The vast majority of patients seeking treatment for insomnia have some kind of sleep breathing problems, at least according to a 2012 study. In that study, published online in the journal Sleep & Breathing, researchers conducted a chart review of 1,035 patients and found that 81 percent had breathing issues.

The study's lead author, Barry Krakow, medical director of Maimonides Sleep Arts and Sciences in Albuquerque, designed a subsequent study to better understand insomniacs without obvious breathing issues -- the 19 percent in his chart review study.

Twenty such people were asked whether they could identify what made them wake up. They reported such causes as nightmares, noises, needing to urinate and pain; many said they didn't know.

Next, the participants spent one night in a sleep research facility. Researchers recorded a combined total of 531 awakenings and found that 478 of them followed a "breathing event" such as an episode of apnea or labored breathing. Thirty awakenings lasted at least five minutes, and all of these were preceded by a breathing event. These findings, published last year in the journal Sleep, reveal that breathing issues are the cause for even more middle-of-the-night awakenings than previously appreciated.

Krakow says studies have tended to focus on getting people back to sleep, not on why they wake up, and "it kept irking me that we couldn't find the cause.

"I believe ... that in people without known causes of insomnia" -- such as stress, depression or other medical conditions -- "90 percent of waking events are due to breathing issues," Krakow says.

Disorders that affect chronic insomniacs may not carry over to people with less severe sleep problems, Krakow says. Still, he advises people to take care of their noses, before heading to the drugstore in search of sleep medication. Treat any allergies, clear your nasal passages with a saline flush or a neti pot, or try nasal strips, which hold the nostrils open.

What might other causes be?

At the sleep center at Howard County General Hospital in Maryland, Charlene Gamaldo, a Johns Hopkins neurologist, says she starts her evaluations by asking patients "to give me a play-by-play account of what they do to prepare for sleep, their experience through the night and how they feel the next day. And 99 percent of the time, regardless of individual issues, there's at least one sleep behavior that I can help." High on the list: pre-bedtime routines and bedroom environment.

So, how can you maximize your chances of sleeping through the night?

Get exercise. In a 2011 study published in the Journal of Public Health, researchers using survey data on sleep and exercise found that people who reported getting "any exercise" in the past 30 days were less likely to have complaints about sleep or daytime tiredness.

Avoid TV and tablets right before bed. The body prepares for sleep over a period of three to four hours, Gamaldo says. "There's a whole cascade of events, including the release of melatonin," a hormone that helps regulate sleep cycles. The blue light of television and electronic devices is particularly disruptive to hormones involved in circadian rhythms and can lead to problems initiating and maintaining sleep.

Don't drink to get sleepy. Alcohol can contribute to middle-of-the-night awakenings as well. "The term 'nightcap' is a misnomer," Gamaldo says. "Alcohol does have sedative properties and might help you get to sleep, but it's rapidly metabolized, and when cleared (by your body) can function to wake you up." Gamaldo calls this "rebound insomnia."

Keep your bedroom cool, dark and quiet. "Like a cave," Gamaldo says. "Anything that disrupts that lovely little formula can wake you up in the night." Use window blinds to block streetlights and mute your cellphone.

And if you do wake up in the night? "Once you're awake more than 20 minutes, you should leave the bedroom," Gamaldo says. Go to another room, engage in a relaxing activity, such as listening to music or reading, but keep lighting on the dim side. When you're tired, go back to bed. The process can take an hour or more. "It's an established technique to deal with insomnia," she says. "What you don't want is a negative association between your bed and not sleeping."

Grandner agrees, although he knows it seems counterintuitive to get out of bed in order to sleep. "In the short term, you may sleep less. But it's for long-term gain."

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